1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device of a field sequential driving mode, capable of improving flicker and obtaining a good contrast by optimizing a driving frequency.
2. Description of the Related Art
In general, a color liquid crystal display device includes a liquid crystal panel having upper and lower substrates and liquid crystals interposed between the two substrates, a driving circuit driving the liquid crystal panel, and a backlight providing white light to the liquid crystals. This liquid crystal display devices can be classified into two modes, an RGB (red, green, blue) color filter mode and a color field sequential driving mode, according to a color image displaying method.
The liquid crystal display device for the color filter mode is configured in such a manner that R, G, B color filters are arranged to R, G, B unit pixels respectively into which one pixel is divided. In this configuration, light is transmitted from a backlight through the liquid crystals to the R, G, B color filters, and thus color images are displayed.
By contrast, the liquid crystal display device of the color field sequential driving mode is configured in such a manner that R, G, B backlights are all arranged to one pixel which is not divided into R, G, B unit pixels. In the configuration, three primary colors of light, R, G, B, from the R, G, B backlights are sequentially displayed through the liquid crystals in a time-shared manner, and thus color images are displayed using an after-image effect of the eye.
Because the time interval of one frame generally driven at 60 Hz (hertz) is 16.7 ms ( 1/60 sec), in the field sequential driving mode liquid crystal display device divided into three sub-frames from one frame as described above, one sub-frame has the time interval of 5.56 ms ( 1/180 sec). The time interval of one sub-frame is very short, thereby any field change cannot be visually recognized. Therefore, the human eye may recognize it with an integrated time of 16.7 ms (millisecond), so that the combination of three primary colors, R, G, B, could be visually recognized.
Accordingly, compared with the color filter mode, the field sequential driving mode has advantages in that it can implement a resolution higher than almost three times the color filter mode under the condition that the panels are of the same size, increase the efficiency of light due to not using the color filter, and realize the same color reproduction as a color television and high-speed moving picture. In spite of these advantages, since one frame is divided into three sub-frames, the field sequential driving mode requires a driving frequency higher than six times the color filter driving mode. As such, high-speed operational characteristics are required for the field sequential driving mode.
Currently, in the liquid crystal display device of the digital field sequential driving mode, driving voltages having polarities different from each other are applied to the same pixel during the neighboring frames. Here, absolute values of each driving voltage applied to the same pixels for the neighboring frames are different from each other, so that the amount of transmitted light in the current frame is different from that of transmitted light in the next frame. Thus, the same pixels of the neighboring frames have different brightness, which results in flicker in the image.
Conventionally, the flicker caused by a difference of the amount of transmitted light between the neighboring frames has been prevented by adjustment of a common voltage applied to liquid crystal cells. However, it is difficult to fully prevent the flicker by means of only the adjustment of the common voltage.